The present disclosure relates to signal tracking and, more particularly, to an apparatus and method for tracking a satellite signal.
A global navigation satellite system (GNSS) tracks the location of a target on the ground by using a network of artificial satellites staying afloat in the space. GNSS refers to the general global positioning system (GPS) operated by the U.S. Department of Defense, the Galileo positioning system being developed by the European Union, a global navigation satellite system (GLONASS) operated by Russia, and the like. The GNSS is extensively employed to acquire the location of aircrafts, vehicles, ships, etc. and also adapted for information technologies such as telematics and the like.
Typically, the GPS, a satellite navigation system providing location information by using satellites orbiting in the space, was established for the military purpose at an early stage, and since selective availability, namely, an intentional noise, was removed in 2000, it has been widely employed in various fields. The GPS satellites share frequency bands with different codes by using a code division multiple access (CDMA) scheme.
A GPS receiver measures its location by using signals from at least three satellites. A single tracking module is allocated to a single satellite to acquire a measurement result. The measurement result is data acquired based on satellite signals, which may be three-dimensional rectangular coordinates data on the earth, such as x, y, and z, or data for determining the rectangular coordinates. Conventionally, the GPS receiver includes 12 or 16 tracking modules.
In order to enhance the reliability of the GPS receiver, performance of the tracking modules for tracking satellite signals is critical. The strength of satellite signals may be severely changed due to Doppler effect or a change in a line of sight (LOS) caused by the movement of the GPS receiver. If the tracking modules fail to properly track such change in the satellite signals, a success rate of acquiring the measurement results would be sharply lowered. If a signal sensitivity of the tracking module is reduced, the measurable strength of satellite signals may be reduced so that measurement results cannot be obtained. On the contrary, if the signal sensitivity is increased, a measurement error may be increased.